posted on Feb, 24 2014 @ 09:48 AM
It doesn't necessarily mean what you think it does.
First, some assumptions-
1)There is one universe/timeline/whatever you want to call it. When you time travel, you go to the future or past of a single timeline, no alternates
2)The universe has some sort of "timeline" protection to prevent you from killing your grandfather (google grandfather paradox if it's not clear to
you why this would be a problem). Futurama represented this by having Fry become his own grandfather (i.e. doing the nasty in the past-y)
3)Time travel is accomplished in some kind of Einsteinian way, as opposed to astral projection or computer simulations or anything else.
This assumes that stable wormholes are possible.
The way it works:
Create a wormhole. If said wormhole is enterable and exitable at both ends, you only have to make one.
If it's composed of a black hole and a white hole (or some analogue), you have to create 2- 2 entrances, 2 exits, otherwise you can only travel one
way. Since we're talking about fantastic things anyway, from now on we'll assume you can enter/exit the wormhole at either end and only need to make
Take one end faaaaar away at relativistic speed, and then bring it back, also at relativistic speed.
Due to time dilation, the clocks on the ends of our wormhole are different. One end has been on earth the whole time the other end was in deep space
transit. A long time has passed on earth, not much for the travelling end of the wormhole, meaning that end will exit in the far future, and from
it's point of view, the end that stayed on earth exits in the far past.
The implication of this, if you were following along, is that you can never travel into the past to a time before you built your time machine. There
is no "doorway" to that previous time.
So that could be why there are no time travellers from the future. Time machines haven't been invented yet, and as long as that is the case, there
will never be time travellers from the future.